1. Field of the Invention
The present invention relates to the field of micro pressure sensor, and more particularly, to a manufacturing method for the miniaturization of silicon bulk-machined micro pressure sensors, and the structure of the micro pressure sensor manufactured by such a manufacturing method.
2. Description of Related Art
FIG. 5 shows the structure of a conventional micro-sensor fabricated by silicon bulk-micromachining. Such a micro-sensor is produced by bonding a bulk silicon wafer 51 to a glass substrate 52. A cavity 53 is defined in a first face 511 of the bulk silicon wafer 51 before bonding such that a predetermined portion of the bulk silicon wafer 51 is provided as a diaphragm 54 Multiple resistors 55 and circuit connection (not shown) are formed on a second face 512, which is opposite to the first face 511, of the bulk silicon wafer 51. Normally, there are four resistors 55 located on the edge of the diaphragm 54 so that the pressure asserted on the diaphragm 54 can be measured via the resistors 55. This conventional micro-sensor suffers a disadvantage in that the dimension thereof is difficult to miniaturized. Because of the lattice structure of the bulk silicon wafer 51, it is hardly to define a cavity 53 by known etching technique with side faces 531 perpendicular to the diaphragm 54. Instead, the side faces 531 of the cavity 53 are always inclined with respect to the diaphragm 54, which are known as the (111)-face slopes in the art. Such face slopes will result in wasting of chip area and therefore, prohibit the miniaturization of the silicon bulk-machined sensors.
FIG. 6 shows the structure of another conventional micro-sensor fabricated by silicon bulk-micromachining. This micro-sensor is produced by bonding a first bulk silicon wafer 61 to a second bulk silicon wafer 62. The first bulk silicon wafer 61 is flat and provided as a diaphragm. The second bulk silicon wafer 62 has a cavity 63 defined in an upper face thereof. Multiple resistors 65 and circuit connection (not shown) are formed on the first bulk silicon wafer 61 for sensing the pressure asserted thereon. Because the resistors 65 has to be located on the edge of the cavity 63, an alignment process must be undertaken when forming the resistors 65. Further, since a high temperature annealing process has to be executed after bonding the first bulk silicon wafer 61 to the second bulk silicon wafer 62 to securely combine them together, the resistors 65 can be formed only after the bonding process to avoid being damaged by the high temperature. As a result, because the cavity 63 is inside the combination of the first and second bulk silicon wafers 61, 62 and both of the bulk silicon wafers 61, 62 are non-transparent, it is difficult to form the resistors 65 at desired positions with an alignment process. Therefore, there is a desired to improve the structure and the manufacturing method of the above micro pressure sensors to mitigate and/or obviate the aforementioned problems.